Tree-living ants glide to safety

Canopy-dwelling ants in the tropical forests of the Americas have adopted a neat way of averting disaster should they fall from their perch. They glide to safety, steering towards their home trunk rather than plummeting to the ground, where they might never see their nest-mates again.

Worker ants of the species Cephalotes atratus can glide in a chosen direction if dislodged by the wind or larger animals, Stephen Yanoviak of the University of Florida, Vero Beach, and his colleagues have discovered. By making video recordings of plummeting ants, the researchers showed that they fly backwards, abdomen first, using their oar-shaped hind legs to steer towards the tree.

“They fell down and made a nice J-shaped curve back to the tree.”

Stephen Yanoviak University of Florida

The discovery was an accident, Yanoviak recalls. "About two years ago I was climbing trees to collect mosquitoes when I was attacked by these ants. I brushed 20 or 30 of them off; they fell down and made a nice J-shaped curve back to the tree."

The researchers therefore travelled to the ants' habitats in Panama, Costa Rica and Peru to film the insects' dives after dropping them from branches. As they report in Nature1, the ants' acrobatics allow them to hit their home trunk with 85% accuracy, and be reunited with their fellows within ten minutes.

Fatal fall

This is a useful skill for C. atratus, which lives in colonies that inhabit a single tree, Yanoviak explains. "If they fall to the ground they're lost. That's the assumption," he says. "The rainforest is flooded for half of the year, so if they fall there's no way back. And even if the ground is dry it's pretty hazardous for them, with predators and unfamiliar terrain."

<mediar rid='m1'><?xm-replace_text {mediar}?></mediar>"It would be nice to know how frequently they do it in the wild," comments Nigel Franks, who studies ant behaviour at the University of Bristol, UK. Other ants, such as the African army ant Dorylus, will drop from trees, but they always end up on the ground, he adds.

The remarkable self-preservation instincts of C. atratus may be a product of their small colony sizes, Franks suggests. "In small colonies we tend to think of individual workers as more valuable per capita," he explains.

But before trying to explain their behaviour, it might be best to check that gliding actually does come naturally to the ants, suggests Stuart Hine, an entomologist at the Natural History Museum in London. "I would like to see these drop tests done in the laboratory, where there are no winds," he says.

Gifted gliders

Although these are the first insects to be hailed as directional gliders, Yanoviak is confident that more will be discovered among the many thousands of insect species. "Nobody, not even a biologist, would have expected this," he says. "But now I guarantee that we will see more non-ant insects that glide."

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Franks, meanwhile, remains fascinated by the unexplored mysteries of tree-living ants. "There are so many ants in the canopy of rainforests," he enthuses. "It won't be surprising if we see more beautifully evolved behaviours like this."